1. Field of the Invention
This invention relates to a sleeve for pressing rollers, preferably for screen rollers of rotary printing machines consisting of an internal, preferably two-layer tube consisting of expandable material, whose inside diameter is adapted to the diameter of the roller intended to carry said material and that is connected with an outer, dimensionally stable casing tube.
2. Description of the Related Art
In printing with a sleeve of this kind, known from DE 196 13 145 Al, it was observed that the printed surfaces displayed shaded areas and/or areas that were smudged in a trembly pattern; this is presumably due to the fact that the casing tube, retained on the inner tube with a certain elasticity and consisting of expandable material, forms a spring-mass system with said casing tube, which system is made to oscillate particularly in the range of natural frequencies.
The object of the invention therefore is to provide a sleeve of the kind mentioned initially that at all rpm will ensure a good, uniform print without any smudging.
This problem is solved according to the invention in that the casing tube at its terminal areas is provided with carrying discs or bushings that at least have segments whose boreholes are adapted to the diameter of the roller with a snug fit or a pressing fit.
It was now found quite by surprise that the sleeves, designed according to the invention, ensure perfect pressure at all customary roller rpm. This is presumably due to the fact that the casing tube by virtue of the frontal bushings or carrying discs without interjection of the internal tube, in other words, an intermediate layer consisting of elastic material, is connected with the roller so that the elasticity needed for pulling the internal tube upon the roller can no longer introduce any oscillations into the casing tube.
In a practical manner, the casing tube is connected by terminal bushings with the internal tube, where the bushings are provided with blind boreholes into which the carrying discs are fitted. In this design of the invention, the casing tube is connected to the internal elastic widenable tube through the bushing, although in the terminal area of the bushing, there is fitted a carrying disc that connects the casing tube with the roller without the interjection of the internal tube, in other words, without a layer of elastic material inserted in between.
The bushing can have a T-shaped cross-section and the T-bridge is provided with the blind borehole.
The invention-based sleeves are usually pulled on cantilevered rollers. To pull the sleeves up, it is at least required that one layer of the roller be moved so that the sleeve can be pulled on the cantilevered roller. In a practical manner, the internal carrying disc has a larger borehole than the external one so that the internal carrying disc can be pushed almost without any contact over the length of the roller up to a terminal collar of the roller upon which the latter then rests with a snug fit or a pressing fit.
The bushing can be welded together with the casing tube. The carrying disc can be fitted into the borehole of the bushing with a pressing fit or can be connected with it in some other way.
According to another inventive feature, it is provided that the casing tube be connected with the inner tube by means of terminal bushings and that outside-located segments of the bushings in each case rest against the roller with a snug fit or a pressing fit. This embodiment is simplified inasmuch as the casing tube is connected both with the internal tube and the roller only by means of bushings that are made of one part.
In a practical manner, the outer segment of the internal bushing has a larger diameter than the outer segment of the outer bushing. This again makes it simpler to pull the bushing on the roller, something that in a practical manner and in the known fashion is done with compressed air.
The bushings can be connected to the casing tube by means of adhesive connections; furthermore, the bushings can be connected to the internal tube also by means of adhesive connections.
The bushings are usually pulled on by means of compressed air that is supplied through axial and radial boreholes of the roller to the latter""s casing. To prevent the compressed air used for pulling up from resulting in a separation of the adhesive connection between the bushings and the internal tube, a further feature of the invention provides that the bushings in each case be provided with ventilation boreholes that bridge the segments with a snug fit or a pressing fit.
An exemplary embodiment of the invention will be explained in greater detail below with the help of the drawings.